Weather Blog: First 70s of the season looming

Thank you for stopping by the Weather Watch 12 Blog! Spring has played out in slow motion this year with chilly temperatures and persistent rain. Only twice this spring has Milwaukee reached a high of 60 or warmer! That has lead to a chorus of questions asking, "When will we hit 70?" or "Will we get a spring?". In today's Weather Watch 12 Blog we use the LRC to show when warmer temperatures arrive, and how this warm-up was pinpointed back in March!

Let's start with an overview of average monthly temperatures through April 21. The Midwestern Regional Climate Center map below shows all of Wisconsin experiencing below average temperatures this month. The departure from average in Milwaukee is around 4 degrees below average. The cold has combined with snow to drive temperatures to the deep freeze over Minnesota and the Dakotas.

The overall weather pattern which set-up last fall continues to cycle or repeat, driving our current and future weather. The cycling weather pattern is described in a weather pattern theory we use called the LRC, or Lezak's Recurring Cycle. Just yesterday I was fielding questions on Twitter regarding the LRC. Before we show how the LRC allows us to pinpoint a specific warm-up weeks or more in advance, let's go over the basics of the theory.

A unique weather pattern sets up every year between the start of fall and mid-November

Long term long-wave troughs(low pressure) and ridges(high pressure) become established. These dominant repeating features are clues to where storm systems will reach peak strength, and where they will be their weakest.

Once the weather pattern is set it cycles, repeats, and continues through winter, spring and into summer. Identifying the cycle length is key to making long range weather predictions.

The LRC is a 10-11 month pattern! There is a pattern! It isn't just one long-wave trough, storm system, or ridge. It is a sequence of troughs and ridges that are cycling around the Northern Hemisphere

The cycle duration this LRC season(fall-summer) is around 53-51 days. This cycle duration was first identified in last October in the Weather Watch 12 Blog.

?The LRC is easiest to see in the middle of the atmosphere since we are dealing with the large scale flow. The middle of the atmosphere is located at the 500mb pressure level.

Now let's simplify what we just discussed above to show why confidence is growing that the first 70s of the season may be looming. The map below is a 6 day forecast of the 500mb flow next Monday, April 29 at 7am. Since this is a model forecast for the future the features below will change some, but I think this forecast looks pretty good.

The focal points on this map have been labeled with numbers 1-4. The most important feature is 2, a trough over the northern Plains resulting in a southwest wind flow over the Midwest. This southwest flow should push warmer temperatures toward southern Wisconsin.

This is a feature we have seen in past cycles. For our comparison below we will go back 158 days, or 3 cycles(52.66 days per cycle). The map below is valid November 22, 2012. The key features are labeled 1-4, with special attention on 2 -- the trough over the northern Plains leading to a southwest flow.

Clearly looking at this map comparison you can see we are dealing with the same part of the weather pattern. In November and January this part of the pattern produced temperatures well above average.

With the knowledge of past cycles and knowing the duration, pinpointing weather events such as this warm-up moving forward is possible. On March 27 our forecast previewing April 2013 called for this warm-up to return. Here's an excerpt from that blog entry:

Potentially the warmest weather of the entire month arrives around April 26-27. This part of the pattern produced highs in the 50s in January, potentially 70s this time around? The warm-up will be ahead of storm system that may bring rain or thunderstorms to southeastern Wisconsin. Cooler weather will follow around April 28-29.The April forecast above was issued based on a 52 day cycle duration. Right now the cycle duration going back to November is a hair closer to 53 days(remember the cycle duration is around 51-53).

With that said the upcoming warm-up should begin around April 26-27 and likely peak April 28 or 29. This is an example of identifying the weather pattern using the LRC -- then projecting forward to make accurate forecasts weeks or months in advance.

The exact timing of the warm-up will shift slightly in the coming days, but the odds of the first 70s of the season are looking good. The question for Milwaukee is whether a lake breeze would cheat the city from the 70s. Right now I think even Milwaukee will hit 70 during the warm spell. This warm-up will be followed by a cold front and a chance of showers and thunderstorms...also pinpointed a month in advance.

If you have questions regarding the LRC or this part of the pattern please feel free to ask.